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Of 33 organisations monitored by the ICO, Birmingham City Council was also singled out as being particularly bad for delays. The London Borough of Hammersmith and Fulham, the London Borough of Islington, Wolverhampton City Council and Westminster City Council were asked to sign undertakings to improve their performance.
Information Commissioner Christopher Graham said: "Responding promptly to FOI requests is key to delivering citizens' rights. Too many public authorities are taking too long to decide either whether to release information or to refuse requests."
The remaining 26 authorities have maintained or improved their response times sufficiently, and no action is being taken against them.
"I am delighted that over two-thirds of the authorities whose performance we have been monitoring have managed to overcome their problems. However, the remaining authorities have not done enough to convince us that they have a clear and credible plan for getting back on track. Over the next four weeks, we shall be discussing appropriate next steps with them," added Graham.
Earlier this year the government extended the scope of the FOI Act to include Examination Boards, Harbour Authorities, the Local Government Association and the NHS Confederation.